Photoresist and post etch residue cleaning solution

ABSTRACT

A process for cleaning a semi-conductor wafer comprising providing etched wafer containing metal pillars, contacting the etched wafer with a cleaning solution, removing the wafer from the cleaning solution, wherein the resulting wafer is substantially free of post etch residues and photoresist residues without etching the metal pillars by the cleaning solution, the cleaning solution comprising:
         A. a polar aprotic solvent,   B. an inorganic base;   C. a co-solvent for said inorganic base;   D. a unsaturated cycloaliphatic compound having a ring ether group and at least one substituent bearing a primary hydroxyl group; and   E. an organic base comprising an amine compound.
 
The wafer containing photoresist residue or post etch residue can be cleaned by contacting the solution in a spray or immersion.

1. CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 13/651,790filed on Oct. 15, 2012, which claims priority to U.S. ProvisionalApplication Ser. No. 61/557,229 filed Nov. 8, 2011, the disclosures ofwhich are incorporated herein by reference in its entirety.

2. FIELD OF THE INVENTION

The present disclosure relates to a cleaning solution for removingresidues from semiconductor substrates, and particularly to remove postetch residues from wafers.

3. BACKGROUND OF THE INVENTION

The technology of fabricating semiconductor integrated circuits hasadvanced with regard to the number of transistors, capacitors and otherelectronic devices which can be fabricated on a single integratedcircuit chip. This increasing level of integration has resulted in largepart from a reduction in the minimum feature sizes of the integratedcircuits and an increase in the number of layers and functionality whichmake up the integrated circuit. The manufacture of integrated circuitcomponents having this reduced size and the need to reduce productionsteps has placed new demands on all aspects of their productionincluding the removal of resists and related materials with chemicalstripper solutions.

Semiconductor devices for semiconductor integrated circuits or liquidcrystal displays are commonly produced by a process including the stepsof coating a substrate with one or more layers of polymeric resistmaterials to provide a resist film; patterning the photosensitive resistfilm by exposure to light and subsequent development; etching exposedportions of the substrate using the patterned resist film as a mask toform minute circuits; and removing the resist film from the inorganicsubstrate. Alternatively, after forming minute circuits, the post etchresidues can be ashed and the remaining resist residues removed from thesubstrate with a post etch residue remover.

Resist stripping compositions that include aromatic quaternary ammoniumhydroxide such as benzyltrimefhylammonium hydroxide (BTMAH), a solventsuch as an alkylsulfoxide, a glycol and a corrosion inhibitor andnon-ionic surfactant do not completely remove many dry-film resists froma wafer surface. Similarly, compositions which use pyrrolidone-basedsolvents such as N-methylpyrrolidone (NMP) exhibit the same drawback inthat they have not achieved complete removal of many dry-film resistsand have compatibility problems with the photoresists. In general,compositions which include a quaternary ammonium hydroxide astetramethylammonium hydroxide (TMAH) in N-methyl pyrrolidone are notcompatible with cured polyimide layers on the wafer.

The Cu film is adhered to layers underneath typically comprising organicdielectric films using Ti or TiW. Commonly this film is removed also ina dilute acid bath, but may be removed using a high energy plasmaprocess. In addition, it may be beneficial to use a high energy plasmaprocess to remove some of the organic dielectric film for a variety ofreasons, including to improve electrical isolation of the solder bumpsand/or as part of a plasma dicing process.

During the high energy plasma-based process, it is common forphotoresist residues to remain behind. Further, plasma-baseddecomposition products can remain as post etch residues. Finally,organic or organometallic and metal oxides vaporized from the plasmaetching process can sublime onto, or be sputtered onto, or react in thevapor phase with each other and deposit onto, the top of the solderbumps or back onto any of the other features on the semiconductor wafersurface.

In wafer level packaging, solder bumps can be formed using anelectroplating process. Electrical contact for the plating step is madeusing a continuous Cu film to distribute the current across a wafer thatis patterned with a photoresist mask. Metal is plated onto the coppersurface in open features. After plating, the photoresist mask is removedand the continuous Cu film is etched from around the plated metal usinga dilute acid solution to electrically disconnect the solder bumps.

The challenge remains to find a solution which cleans post etchresidues, that is, residues created or resulting from an etching process(e.g. an acid and/or plasma etching process) which can include organicmaterials such as post etch degradation or damaged polyimide, new metaloxides formed such as SnO, and organometallic degradation productscreated from the plasma etching process such as from etching the Tilayer and/or the Sn etch products (collectively the post etch residues).

It is also desirable that this solution not only clean and removephotoresist post etch residues, but also maintains compatibility withpermanent wafer features, such as metals comprising the solder caps(e.g. SnAg) and the copper pillars. A solution which is incompatiblewith the wafer features can result in further undesirably etching thesemetal surfaces including the copper pillars and solder bumps, resultingin yield loss.

The solution also should remain stable as a solution during the cleaningprocess to avoid leaving behind residues. Although solid particulatescan form as byproducts in the solution during the heating and coolingcycle or over time, the particulates should remain in solution and notprecipitate out of solution. Any precipitate byproducts can remain asdeposits on wafer surface and production equipment. Thus, the solutionshould be stable at elevated temperatures encountered during operationand when cooled back to room temperatures.

This application addresses a composition and a process for removingorganic, organometallic, and metal oxides from semiconductor substratesthat have their origin as photoresist residues and etching residues onwafer, solder bump walls, and the top surface of the solder bumps.

4. SUMMARY OF THE INVENTION

There is now provided a new cleaning solution which is stable in aheating cooling cycle, while effectively simultaneously cleaningphotoresist residues and post etch residues.

There is now provided a solution comprising:

-   -   A. a polar aprotic solvent,    -   B. an inorganic base,    -   C. a co-solvent for said inorganic base,    -   D. a unsaturated cycloaliphatic compound having a ring ether        group and at least one substituent bearing a primary hydroxyl        group,    -   E. an organic base comprising an amine compound, and    -   F. a nonionic surfactant bearing at least one ether linkage.

There is also provided a process comprising contacting an etched wafercontaining etching residues with a cleaning solution to remove post etchresidues, including solder bump residues, from the entire wafer surfacewithout etching metal on the wafer. The cleaning solution used in thisprocess is desirably the cleaning solution formulation noted above.

5. DETAILED DESCRIPTION OF THE INVENTION

The terms “coating” and “deposition” are used interchangeably throughoutthis specification. The terms “residue” include the photoresist residuesbefore etching an etch residues that include the photoresist byproductsof the etching process, deposits on the solder caps, and otherorganometallic residues of Ti or Cu etching unless specific reference ismade type of residue. The terms “stripping”, “removing”, and “cleaning”are used interchangeably throughout this specification. Likewise, theterms “stripper” and “cleaning composition” are used interchangeably.The term “coating” is defined as a method for applying a film to asubstrate such as spray coating, puddle coating, slit coating orimmersing. The indefinite articles “a” and “an” are intended to includeboth the singular and the plural. All ranges are inclusive andcombinable in any order except where it is clear that such numericalranges are constrained to add up to 100%, and each range includes allthe integers within the range. The terms “weight percent” or “wt %” meanweight percent based on the total weight of the solution, unlessotherwise indicated.

The solution of the invention is effective to remove post etch residues.The solution of the invention can be used to remove residues, includingphotoresists, etch residues, and the like in a variety of other standardapplications including, but not limited to (i) negative and positiveresist removal in wafer level packaging, (ii) post etch residue,including acid and plasma etch residues, for wafer level packaging,plasma dicing, back end of line and for front end of line applications,(iii) plasma dicing operations and (iv) rework.

The solution of the invention is effective to clean residues from asubstrate, for example, an electronic device substrate such as a wafer,which may exhibit irregular topography that includes various layers andstructures such as metal, semiconductor, dielectric and polymericmaterials. Typical semiconductor wafer materials include, for example,materials such as silicon, gallium arsenide, indium phosphide, sapphirematerials, as well as glass and ceramic.

The compositions and methods have particular applicability tosemiconductor wafer fabrication, for example, in the removal of organicfilms and residues from semiconductor wafers. Such organic substancesare present, for example, on post-etched wafers during front-endprocessing or in back-end wafer-level-packaging during a wafer bumpingprocess. The compositions and methods are particularly suitable for theremoval from wafers of hard-to-remove materials such as dry filmphotoresists and post etch residues.

While the present invention provides stripping compositions and methodswhich can effectively remove polymeric organic substances from asubstrate, it is also adapted for removing photoresists that includepositive-tone of both novolac (i.e. cresol formaldehyde) and polyhydroxystyrene (Phost), negative-tone varieties to include acrylics, isoprene(i.e. rubber), as well as dielectrics to include polyimide,polybenzoxazole (PBO), and bisbenzocyclobutene (BCB) but be compatiblewith cured polyimides, polybenzoxazole (PBO), and bisbenzocyclobutene(BCB). The stripping compositions and methods can also remove otherphotoresists, for example multi-layer photoresists and chemicallyamplified photoresists. These organic substances are employed in thefabrication of substrates, for example, the electronic devices onsubstrates such as wafers or flat panel displays, which may includevarious layers and structures such as metal, semiconductor, and theassociated organic materials.

The solution of the invention is effective even at cleaning thedifficult to remove uncured polyimide resist material while beingcompatible with cured polyimide.

The solution of the invention preferably has a flash point above theoperational temperature used to clean the wafer. The solution of theinvention can have a flash point that is at least 75° C., or at least80° C., or at least 85° C., or at least 90° C.

The solution viscosity should be low to permit easy rinsability of thesolution from the wafer surface. In one embodiment, the solutionviscosity, at 25° C., is less than 20 centipoise (cps), or less than 15cps, or less than 10 cps, or less than 8 cps, or less than 5 cps, orless than 4 cps, or less than 3 cps, or less than 2 cps, or less than1.5 cps.

The solution comprises

-   -   A. a polar aprotic solvent,    -   B. an inorganic base;    -   C. a co-solvent for said inorganic base,    -   D. a unsaturated cycloaliphatic compound having a ring ether        group and at least one substituent bearing a primary hydroxyl        group,    -   E. an organic base comprising an amine compound, and    -   F. a nonionic surfactant bearing at least one ether group.

A. The Polar Aprotic Solvent

Polar aprotic solvent compounds are known by those of skill. They arecharacterized as polar, do not have a readily dissociable H⁺ or anacidic hydrogen, do not display hydrogen bonding, and are able tostabilize ions.

The polar aprotic solvent can comprise a C₁-C₁₆ dialkyl sulfoxide, or aC₁-C₈ dialkyl sulfoxide, or a C1-C4 dialkyl sulfoxide, or a C1-C2dialkyl sulfoxide, or dimethyl sulfoxide. The dialkyl sulfoxides, andespecially DMSO, are desirable because they effectively penetrate intothe uncured photoresist and are compatible with the cured polyimidephotoresist that are intended to remain on the semiconductor wafer.Further, a fluorinated plasma etching tends to damage the underlyingcured polyimide layer on the wafer. These post plasma etch damaged curedpolyimide layers are less susceptible to attack and further dissolutionwhen using dialkyl sulfoxides such as DMSO when in combination with theinorganic base such as KOH.

In one embodiment, the solution contains less than 8 weight percentcompounds containing pyrrolidone moieties, or less than 3 wt. %, or hasno compounds added that contain pyrrolidone moieties. Such compounds canhave a tendency to gel the solution upon cooling after heating to 93° C.

The aprotic polar solvent is present in an amount of at least 60 wt. %,or at least 65 wt. %, or at least 65 wt. %, or at least 70 wt. %, or atleast 73 wt. %, or at least 75 wt. %, or at least 78 wt. %, or at least80 wt. %, or at least 83 wt. %, or at least 85 wt. %, and up to 95 wt.%, or up to 93 wt. %, or up to 90 wt. %, or up to 87 wt. %, or up to 85wt. %.

In another embodiment, the polar aprotic solvent is a type present in anamount in the solution effective to remove:

-   -   (i) uncured polyimide photoresist from a semiconductor wafer and    -   (ii) polyimide polymer residues on the semiconductor wafer that        have been subjected to a plasma etching process,        at one or more temperatures within a range of 75° C. to 90° C.        and within 150 minutes, or even within 90 minutes, or even        within 60 minutes, when immersed in the solution. Examples of        such polar aprotic solvents include the dialkyl sulfoxides, in        combination with the other ingredients of the solution of the        invention, are effective at accomplishing these objectives.

B. The Inorganic Base

The inorganic base is reactive with the photoresist and/or post etchresidues and aids in its removal along with the aprotic polar solvent.It is believed that the inorganic base breaks down the molecular weightof the photoresist and/or post etch residues. Organic residues on thesemiconductor wafer are often crosslinked when a plasma etching processis applied and therefore difficult to remove. The inorganic base assistsin the removal of photoresist and the residues generated from a plasmaetching process or other etching processes leaving organic ororganometallic post etch residues.

The type and amount of the inorganic base should be determined on thebasis of its ability to clean, go into solution, and remain in solutionunder a heating/cooling cycle.

Suitable inorganic bases comprise the hydroxides of a Group I or GroupII metal. For solubility reasons, Group 1 metals are preferred. Examplesof the alkali bases that can be mentioned are potassium hydroxide,sodium hydroxide, cesium hydroxide, rubidium hydroxide, and for thealkaline earth bases barium hydroxide, calcium hydroxide, strontiumhydroxide, and magnesium hydroxide. Of these, potassium hydroxide ispreferred for its solubility going into solution, stable in solution,and ability to clean without leaving residues of potassium.

The solution of the invention desirably does not precipitate solidscontaining the metal of the inorganic base upon heating with slowagitation to 93° C. for 2 hours and allowed to cool down under ambientconditions to 23° C. The amount of the inorganic base used should beadjusted to effectively clean the wafer while maintaining a stablesolution.

In another embodiment, the inorganic base selected is a compound thatremoves an uncured polyimide layer on a semiconductor wafer within 150minutes, or within 90 minutes, or within 60 minutes at one or moretemperatures within a range of 75° C. to 90° C.

Suitable amounts of inorganic base in the solution are at least 0.5 wt.%, or at least 0.7 wt. %, or at least 0.9 wt. %, or at least 1.0 wt. %,or greater than 1.0 wt. %, or at least 1.1 wt. %, or at least 1.2 wt. %,or at least 1.3 wt. %, or at least 1.4 wt. %, or at least 1.5 wt. %, andup to 3.0 wt. %, or up to 2.5 wt. %, or up to 2.4 wt. %, or up to 2.3wt. %, or up to 2.2 wt. %, or up to 2.1 wt. %, or up to 2.0 wt. %, or upto 1.9 wt. %, or up to 1.8 wt. %, or up to 1.7 wt. %, or up to 1.6 wt.%, or up to 1.5 wt. %.

In the case of using KOH, it is desirable to use at least 1.0 wt. %. Ithas surprisingly been found that in a heat/cycle test, a solutioncontaining less than 1.0 wt. % was not stable and precipitated out ofsolution.

In another embodiment, the solution does not contain added lithiumhydroxide for solubility reasons.

C. The Co-Solvent

The co-solvent solvates the inorganic base in the polar aprotic solventat 25° C. Without this co-solvent, the inorganic base precipitates outof solution over time or in heat/cool cycles. The co-solvent and amountselected is also compatible with cured polyimides so as not to removethe polyimide that should remain on the wafer. Further, the co-solventtype and amount should have the capacity to effectively clean coppersidewalls, be rinseable, not etch the metal, and not leave behind anydeposits.

The co-solvent comprises a glycol ether compound having at least oneether linkage and at least one hydroxyl group. Desirably, the co-solventhas one or two ether linkages, and one or two hydroxyl group. An exampleincludes a glycol ether that has one ether linkage and one hydroxylgroup. The hydroxyl group can be a secondary or primary, and desirablyhas a primary hydroxyl group.

In one embodiment, the co-solvent has a molecular weight of less than500, or less than 400, or less than 300, or less than 250, or up to 200,or up to 190, or up to 180, or up to 160.

Examples of co-solvents that have an ether group and a hydroxyl groupcan be represented by any one of the following structures:

R^(4′)—C0₂C₂H₄OC₂H₄—OR⁴,  (II)

R^(5′)C0₂C₃H₆OC₃H₆—OR⁵  (III)

R⁶OC0₂R⁷  (IV)

R⁸OC₂H₄OC₂H₄OH,  (V)

R⁹OC₃H₆OC₃H₆OH,  (VI)

R¹⁰OC2H₄OH,  (VII)

or

R¹¹OC₃H₆OH,  (VIII)

wherein R⁴, R^(4′), R⁵, R^(5′), R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ areindependently selected from C₁-C₁₄ alkyl groups, or C₁ to C₈ alkylgroups.

Examples of co-solvent within formulae (II)-(VIII) includeethyleneglycol monomethyl ether, ethyleneglycol monoethyl ether,propylene glycol monomethyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol monopropyl ether,diethylene glycol monobutyl ether, dipropylene glycol monobutyl ether,dipropylene glycol monopropyl ether, tripropylene glycol monomethylether, tripropylene glycol monobutyl ether, propyleneglycol butyl ether,ethylene glycol monohexyl ether, ethyleneglycol mono-2-ethylbuyl ether,triethyleneglycol monobutyl ether, tetraethyleneglycol monobutyl ether,or tetrapropyleneglycol monobutyl ether, or combinations thereof.

In another embodiment, the co-solvent comprises a compound representedby the following formula (IX):

wherein R¹ and R³ are each independently be a hydrogen atom or a C₁-C₁₂alkyl group, or a C₁-C₈ alkyl group, or a C₁-C₆ alkyl group, or a C₁-C₄alkyl group, or a C₁-C₂ alkyl group, and R² is a C₁-C₁₂ alkyl group, ora C₁-C₈ alkyl group, or a C₁-C₆ alkyl group, or a C₁-C₄ alkyl group, ora C₁-C₂ alkyl group. For example, R¹ can be a C₁-C₄ alkyl group, or aC₁-C₂ alkyl group, R³ can be hydrogen, and R² can be a C₁-C₄ alkylgroup, or a C₁-C₂ alkyl group. Examples of co-solvents within formula(IX) include 3-methoxybutanol; 3-methyl-3-methoxybutanol; and3-methyl-1,3-butanediol, and combinations thereof.

In another embodiment, the co-solvent can be represented by thefollowing general formula (I):

R¹²O(C₂H₄)_(m)(C₃H₆O)_(n)R¹³

wherein R¹² and R¹³ each individually are a hydrogen atom or an alkylgroup having 1-8 carbon atoms, provided that R¹² and R¹³ are not bothhydrogen atoms, m and n stand individually and independently for aninteger of 0-10 provided that m plus n does not equal zero. Desirably, nequals zero, and m is an integer between from 1 to 8, or 1 to 6, or 1 to4, or 1 to 3, or 1 to 2, and R¹³ is hydrogen. The polymer can be arandom or block copolymer.

The co-solvent is present can be present in the solution in an amount ofup to 15 wt. %, or up to 10 wt. %, or up to 8 wt. %, or up to 7 wt. %,or up to 6 wt. %, and at least 1 wt. %, or at least 2 wt. %, or at least3 wt. %, or at least 4 wt. %. The particular amount selected for a givenco-solvent should be effective to solubilize the inorganic base whileproviding a clean surface finish on copper sidewalls.

Care is taken to balance the amount of the co-solvent with the amount ofthe inorganic base to avoid the precipitating solids from solution andto avoid an excess of co-solvent which can inhibit cleaning. Theinorganic base can react with the co-solvent at the primary hydroxylsite to form a salt of the co-solvent, and if a large excess of each arepresent in solution, the solution becomes unstable and may precipitateupon cooling. Therefore, the amount of co-solvent and inorganic baseselected are effective to avoid precipitating solids when subjected to atest comprising heating with slow agitation to 93° C. for 2 hours andcooled to 23° C. under ambient conditions.

D. The Unsaturated Cycloaliphatic Compound

The solution also contains an unsaturated cycloaliphatic compound havingan ether group in the ring and at least one substituent bearing aprimary hydroxyl group. This compound desirably does not react with theinorganic base at 93° C. to any significant extent and does not have atendency to form precipitates. The unsaturated cycloaliphatic compoundcleans the top of the solder bumps that contain tin/silver solder. Thesetypes of deposits often include metal oxides which can form when plasmaetching vaporized metal and the vaporized metal sublime or react withsurrounding oxygen onto the tops of the solder bumps. Organometalliccompounds can also sublime onto the tops of the solder bumps.

The amount of the unsaturated cycloaliphatic compound used is sufficientto clean the caps of the solder bumps without etching the metal. If toomuch is used, the pillars, solder bumps, and/or the Ti or Ti/W gluelayer can be etched and pitted.

The unsaturated cycloaliphatic compound can be present in the solutionin an amount ranging from at least 1 wt. %, or at least 2 wt. %, or atleast 2.5 wt. %, or at least 3 wt. %, or at least 3.5 wt. %, or at least4 wt. %, and up to 8 wt. %, or up to 7 wt. %, or up to 6.5 wt. %, or upto 6 wt. %, or up to 5.5 wt. %, or up to 5 wt. %, or up to 4.5 wt. %, orup to 4 wt. %.

An example of an unsaturated cycloaliphatic compound can be representedby the following general formula (X):

wherein R¹⁴ and R¹⁵ are independently hydrogen, a hydroxyl group, or abranched or unbranched C₁-C₈ alkyl group having one or more primary orsecondary hydroxyl groups, provided that R¹⁴ and R¹⁵ are not bothhydrogen and are not both hydroxyl groups. Desirably, R¹⁴ is hydrogenand R¹⁵ is an unbranched C₁-C₈ alkyl group, or a C₁-C₈ alkyl group, or aC₁-C₆ alkyl group, or a C₁-C₄ alkyl group, or a C₁-C₂ alkyl group, eachhaving a primary hydroxyl group.

Examples of the unsaturated cycloaliphatic compound includetetrahydrofurfuryl alcohol, furfuryl alcohol, or a combination thereof.

E. The Organic Base

The solution contains an organic base that contains an amine group. Theorganic base effectively aids in decomposition reactions and ischemically compatible with and solvates the degradation product residueson the wafer. The organic nature of the base helps solvate the organicresidues.

The organic base is desirably a liquid at 25° C. Desirably, the organicbase is an alkanolamine compound.

The alkanolamine desirably has at least two carbon atoms, at least onenitrogen atom, and at least one hydroxyl group, the nitrogen atom andhydroxyl group being attached to different carbon atoms.

Examples of alkanolamines include ethanolamine, N-methylethanolamine,N-ethylethanolamine, N-propylethanolamine, N-butylethanolamine,diethanolamine, triethanolamine, N-methyldiethanolamine,N-ethyldiethanolamine, isopropanolamine, diisopropanolamine,triisopropanolamine, N-methylisopropanolamine, N-ethylisopropanolamine,N-propylisopropanolamine, 2-aminopropane-l-01,N-methyl-2-aminopropane-l-ol, N-ethyl-2-aminopropane-l-01,1-aminopropane-3-01, N-methyl-l-aminopropane-3-01,N-ethyl-laminopropane-3-01, 1-aminobutane-2-01,N-methyl-laminobutane-2-01, N-ethyl-l-l-aminobutane-2-01,2-aminobutane-l-01, N-methyl-2-aminobutane-l-01,N-ethyl-2-aminobutane-l-01, 3-aminobutane-l-01,N-methyl-3-aminobutane-l-01, N-ethyl-3-aminobutane-l-01,1-aminobutane-4-01, N-methyl-l-aminobutane-4-01,N-ethyl-l-aminobutane-4-01, 1-amino-2-methylpropane-2-01,2-amino-2-methylpropane-l-01, 1-aminopentane-4-01,2-amino-4-methylpentane-l-01, 2-aminohexane-l-01, 3-aminoheptane-4-01,1-aminooctane-2-01, 5-aminooctane-4-01, 1-aminopropane-2,3-diol,2-aminopropane-l,3-diol,tris(oxymethyl)aminomethane,2-(2-aminoethoxyl)ethanol, ethers of alkanolamines, and combinationsthereof.

In an embodiment, the organic base has 2 or fewer hydroxyl groups, aprimary hydroxyl group, and 6 or fewer, or 5 or fewer, or 4 or fewercarbon atoms, such as monoethanolamine, N-methylethanolamine,N-ethylethanolamine, N-propylethanolamine, N-butylethanolamine,diethanolamine, methyldiethanolamine, and N-ethyldiethanolamine.

The amount of the organic base in the solution is at least 1 wt. %, orat least 1.5 wt. %, or at least 2 wt. %, or at least 2.5 wt. %, and upto 5 wt. %, or up to 4.5 wt. %, or up to 4.0 wt. %, or up to 3.5 wt. %.An excess can turn the solution turbid and risk the formation ofprecipitating solids out of solution.

F. The Surfactant

The solution contains a nonionic surfactant that contains at least oneether linkage. The surfactant is effective to prevent precipitation andto keep the solution stable.

In an alternative embodiment, the surfactant has an HLB number of atleast 8, or at least 8.2, or at least 8.3, or at least 9, or at least10, or at least 12, and up to 18, or up to 16, or up to 15, or up to 14,or up to 13.

The surfactant can have a molecular weight of greater than 200, or atleast 250, or at least 300, or at least 400, or at least 500, and up to2000, or up to 1500, or up to 1000, or up to 900, or up to 850, or up to800, or up to 750, or up to 700, or up to 650, or up to 600, or up to550, or up to 500, or up to 450.

The surfactant is desirably a liquid at 25° C. and has a viscosity ofless than 200 centipoise, or less than 150 cps, or less than 120 cps, orless than 100 cps, or less than 80 cps, or less than 60 cps, or lessthan 40 cps, or less than 20 cps, or less than 10 cps.

The amount of surfactant should be sufficient to keep a stable solution.The amount of surfactant is at least 1 wt. %, or at least 2 wt. %, or atleast 3 wt. %, or at least 3.5 wt. %, or at least 4 wt. %, or at least4.5 wt. %, and up to 10 wt. %, or up to 8 wt %, or up to 7 wt. %, or upto 6 wt. %.

In an embodiment, the surfactant has an aromatic ring having at leastone substituent, said substitutent containing a —(C2H4O)p- moiety, wherec is an integer ranging from at least 1, or at least 2, or at least 3,or at least 4, or at least 5, or at least 6, or at least 8, or at least10, and up to 50, or up to 40, or up to 30, or up to 20, or up to 15, orup to 10, or up to 8, or up to 6.

The surfactant may also contain an aromatic ring having a firstsubstitutent containing —(C₂H₄O)— moieties and second substituentcomprising a branched or unbranched, saturated or unsaturated, C₁-C₂₂alkyl group, or a C₁-C₁₂ alkyl group, or a C₁-C₁₀ alkyl group, or aC₁-C₉ alkyl group, or a C₁-C₇ alkyl group, or a C₁-C₄ alkyl group.

The surfactant desirably contains a polyoxyalkylene (EO preferred)derivative of a phenolic compound which can be substituted with anbranched or unbranched alkyl group. Phenol ethoxylates are non-ionicsurfactants, consisting of a phenol or a branched-chain alkylphenolwhich has been reacted with ethylene oxide, producing an ethoxylatechain. Commercial formulations are usually a complex mixture ofhomologues, oligomers and isomers. Examples of common alkylphenols arenonylphenol ethoxylates and octylphenol ethoxylates. Examples ofrepeating EO units are 4, 6, 7, 8, 9, and 10.

If an alkyl phenolic compound is used to react with EO, suitableexamples include cresol, ethylphenol, propylphenol, butylphenol,amylphenol, hexylphenol, heptylphenol, octylphenol, nonyl phenol,decylphenol, dodecylphenol, tetradecylphenol, octadecylphenol, theirmixtures or their isomers. Olefins useful in preparation of thesealkylphenols may contain odd or even number carbon atoms which may be anadvantage in many applications. Mixtures of a-olefins having variousranges of carbon atoms such as C6-C7, C7-C9, C9-Cn, Cn-C15, C15-C20 andhigher may be used in the preparation of these alkylphenols. Olefinscontaining even number carbon atoms such as those derived from fats arealso useful. Likewise, the di- and trialkyl substituted derivatives ofthe aforementioned alkylphenols may be used, such as diisobutylphenol,diamylphenol, dinonylphenol, didodecylphenol, dioetadecylphenol,tri-t-butylphenol, trinonylphenol and the like.

Specific examples of the surfactant include the following compounds, inwhich EO means ethylene oxide and the number is the number moles of EOreacted with one mole of the phenolic compound: phenol+1 EO or 2 EO or3EO or 4 EO or 5 EO or 6 EO or 8 EO or 9 EO or 10 EO,dioetadecylphenol+10 EO, phenol+10 EO, o-cresol+20 EO,diisobutylphenol+30EO, nonylphenol+1 EO or 2 EO, or 3 EO or 4 EO or 6EO, diamylphenol+8 EO, dodecylphenol+20 EO, diamylphenol+150 EO,hexylphenol+15 EO, octadecylphenol+20 EO, and nonyl phenol+50 EO.

Additionally, water may be present in the solution. Often, water will bepresent in the solution as a result of water present in one or more ofthe additives combined together to make the solution. Desirably, wateris not separately added to the solution but can be present in thesolution as a result of its presence in an aqueous formulation of anadditive other than water or if an additive is hydroscopic and picks upatmospheric moisture. Water may be present in the solution in amount ofless than 2 wt %, or less than 1 wt. %, and at least 0.1 wt. %. Toreduce the water content of the solution, one can subject the solutionto a vacuum and backfill with an inert gas. One can also warm thesolution to improve water vaporization.

Examples of formulations include:

-   -   A. dialkyl sulfoxides such as dimethylsulfoxide;    -   B. an alkali metal hydroxide such a potassium hydroxide;    -   C. one or more glycol ethers such as those represented by one or        more of the following formulas:

R⁸OC₂H₄OC₂H₄OH,  (V)

R⁹OC₃H₆OC₃H₆OH,  (VI)

R¹⁰OC₂H₄OH,  (VII)

or

R¹¹OC₃H₆OH,  (VIII)

wherein R⁴, R^(4′), R⁵, R^(5′), R⁶, R⁷, R⁸, R⁹, R¹⁰, and R¹¹ areindependently selected from branched or unbranched C₁-C₁₄ alkyl groups,or C₁ to C₈ alkyl groups, and can include ethyleneglycol monomethylether, ethyleneglycol monoethyl ether, propylene glycol monomethylether, diethylene glycol monomethyl ether, diethylene glycol monoethylether, diethylene glycol monopropyl ether, diethylene glycol monobutylether, dipropylene glycol monobutyl ether, dipropylene glycol monopropylether, ethylene glycol monohexyl ether, ethyleneglycol mono-2-ethylbuylether, triethyleneglycol monobutyl ether, tetraethyleneglycol monobutylether, or tetrapropyleneglycol monobutyl ether, or combinations thereof;oror those represented by formula (IX):

wherein R¹ and R³ are each independently be a hydrogen atom or a C₁-C₆alkyl group, R² is a C₁-C₆ alkyl group, and can include3-methoxybutanol; 3-methyl-3-methoxybutanol; 3-methyl-1,3-butanediol, orcombinations thereof.

-   -   D. a compound having a furfuryl moiety and containing primary        hydroxyl group such as tetrahydrofurfuryl alcohol;    -   E. an alkanolamine; and    -   F. a nonionic surfactant obtained by the reaction of a phenol or        alkyl phenol with ethylene oxide.

In each of the ingredients A-F, the compounds are different and distinctfrom each other. In other words, a single compound does serve toconstitute two or more of the ingredients A-F.

The amounts of each compound A-F in the solution of the invention canbe:

-   -   A: at least 73 wt. %, or at least 75 wt. %, or at least 78 wt.        %, or at least 80 wt. %, up to 87 wt. %, or up to 85 wt. %; and        ranges can include 73-87, or 75-87, or 80-87, each in wt. %;    -   B. at least 1.0 wt. %, or greater than 1.0 wt. %, or at least        1.1 wt. %, up to 1.6 wt. %, or up to 1.5 wt. %, or 1-1.6, each        in wt. %;    -   C. up to 10 wt. %, or up to 8 wt. %, or up to 7 wt. %, and at        least 3 wt. %, or at least 4 wt. %, or 3-10, or 4-8, each in wt.        %;    -   D. at least 2.5 wt. %, or at least 3 wt. %, or at least 3.5 wt.        %, up to 6.5 wt. %, or up to 6 wt. %, or up to 5.5 wt. %, or        2.5-6.5, or 3-6, or 3.5-6;    -   E. at least 2 wt. %, or at least 2.5 wt. %, and up to 5 wt. %,        or up to 4.5 wt. %, or up to 4.0 wt. %, 2-5, or 2-4.5, or 2-4,        each in wt. %; and    -   F. at least 2 wt. %, or at least 3 wt. %, or at least 3.5 wt. %,        up to 7 wt. %, or up to 6 wt. %, or 2-7 or 3-6, each in wt. %.

There is also provided a method of cleaning semiconductor wafers usingthe solution of the invention.

In typical processes, the wafer is immersing in a bath of the cleaningsolution. Agitation of the composition in the bath additionallyfacilitates photoresist removal. Agitation can be effected by mechanicalstirring, circulating, by bubbling an inert gas through the composition,or any combination thereof. Upon removal of the desired amount of resistand residues, the substrate is removed from contact with the cleaningsolution and rinsed with water, an alcohol, or a mixture thereof. DIwater is a preferred form of water and isopropanol is a preferredalcohol. Water is the preferred rinsing agent. For substrates havingcomponents subject to oxidation, rinsing can be done under an inertatmosphere.

In addition to immersion techniques, wafers can also be contacted with astripper solution utilizing a spray device with the stripper solutionmaintained at the desired temperature, or a combination of immersion andspray. The spraying can optionally be carried out using additionalcleaning aids including ultrasonics and/or under an inert atmosphere oroptionally in the presence of an active gas such as, for example, oxygenor ozone. The wafer can be removed periodically and inspected todetermine when sufficient cleaning has occurred. The clean wafer can berinsed with isopropanol and dried.

Additionally, wafers containing a single layer of negative thickphotoresist dry film, or single layer of negative or positiive spin onfilm, and resist stacks having one or multiple layers of positive and/ornegative resists can also be processed by these methods. Typical resiststacks can include, but are not limited to, one or multiple layers ofresist which can include, for example, a planarizing layer, a bottomantireflection coating layer, a hard mask, and/or a photoresist.

In one process of the invention, there is provided an etched wafer (e.g.by plasma or dilute acid) containing metal pillars, wherein the etchedwafer is brought into contact with a cleaning solution and cleaned suchthat the wafer is substantially free of residues including post etchresidues (such as solder bump residues) and photoresist residues withoutetching the metal pillars. The contact can be via immersion or spraytechniques.

In another process according to the present invention, one can:

-   -   1. Provide a wafer having a substrate, a cured polyimide layer,        a Ti or Ti/W seed layer, a copper seed layer, a photoresist        layer, copper pillars, and solder bumps;    -   2. Remove photoresist from a bumped wafer containing a        photoresist;    -   3. Remove the copper seed layer, such as through a dilute acid        etch,    -   4. Selectively remove the Ti or TiW film on the wafer though a        plasma etch or in a dilute acid etch,    -   5. Plasma etch from about 1 to 1.5 microns of uncured polyamide        layer on the wafer, wherein step 4 and 5 can occur        simultaneously; and    -   6. Contact the plasma etched wafer with the solution of the        invention to remove all residues.

Once the substrate is submerged in the solution or the solution isapplied and covers, or coats, the entire area, the substrate can beheated or the solution can be applied hot, desirably the latter.Operationally, the solution is preferably maintained at a temperature ata temperature under the flash point of the solution when contacted withthe substrate wafer. The solution of the invention preferably has aflash point above the operational temperature used to clean the wafer.The solution of the invention can have a flash point that is at least75° C., or at least 80° C., or at least 85° C., or at least 90° C., anddesirably at 80° C. or more, or at least 85° C. or at least 90° C.

The wafer can be in contact with the cleaning solution for a period offrom about 10 minutes to 150 minutes, or 45 minutes to 90 minutes. Thevariability in time is dependent upon the material to be removed, itsthickness, and exposure condition.

The rinsing agent used for rinsing can be at a temperature of about 5°C. to about 100° C. However, rinsing can also occur at room temperature.

Example 1

Table 1 sets forth cleaning composition formulations used in thefollowing examples.

TABLE 1 Residue Removal Formulations [1] [2] [3] [4] DMSO, DMSO, 82%DMSO, 80.5% DMSO, 80.5 84.5% MEA, 3% MEA, 4% MEA, 2.8% MEA, 2.8% DB, 11%MMB, 10% MMB, 10.5% MMB, 6.7% H₂O, 0.3% (C₂H₄O)_(n)C₁₈H₃₄O₃, PhenolPhenol 3% ethoxylate, 4.7% ethoxylate, 4.7% KOH, 1.2% H₂O, 0.2% H₂O,0.4% THFA, 3.8% KOH, 0.8% KOH, 1.1% H₂O, 0.4% Ethylsilicate, 0.02% KOH,1.1% [5] [6] [7] [8] DMSO. 80.4% DMSO, 84.5% DMSO, 84.5% DMSO, 84.5%MEA, 2.8% MEA, 14% MEA, 3% MEA, 3% MMB, 10.5% H₂O, 0.3% DM, 11% MMB, 7%DM, 1.9% KOH, 1.2% H₂O, 0.3% THFA, 4% (C₂H₄O)_(n)C₁₈H₃₄O₃, KOH, 1.2%H₂O, 0.4% 3% H₂O, 0.2% KOH, 1.1% KOH, 1.2% Ethylsilicate, 0.02% DMSO:dimethyl sulfoxide MEA: monoethanolamine MMB: 3-methoxy-3-methylbutanolDM: diethylene glycol methyl ether (C₂H₄O)_(n)C₁₈H₃₄O₃: Obtained asDisperbyk 192 rom BYK Chemie KOH: potassium hydroxide THFA:tetrahydrofurfuryl alcohol Phenol Ethoxylate: 4 EO moles nominal

Example 1

The components for the formulations tested, [1-8] in the followingExamples were combined with stirring at room temperature to give between100 and 300 g of a homogenous stripper solution. Solution homogeneityrequires the KOH to be blended into the appropriate co-solvents prior toaddition of DMSO. The surfactant is added into the blend last. Thesolution was heated to 93° C., with slow agitation for 2 hours. Thetimer was started when the solution reached the desired temperature. Thesolution was then removed from the heat source and left to cool to roomtemperature, 23° C. Observations about solution clarity and amount ofprecipitate were recorded in Table 2.

Example 2

The components for the formulations tested in the following Exampleswere combined with stirring at room temperature to give between 100 and300 g of a homogenous stripper solution. Solution homogeneity requiresthe KOH to be blended into the appropriate co-solvents prior to additionof DMSO. The surfactant is added into the blend last. The solution washeated to between 93° C., with slow agitation. Patterned test waferswith solder bumps positioned as an array in a polyimide film wereobtained. The test wafers had been processed in a high energy oxidizingplasma to remove about 1-3 μm of polyimide. Residues deposited on thesides and tops of solder bumps during a plasma process were not removedprior to these tests. The patterned test wafers were cleaved into ˜4×3cm pieces and mounted into a small scale wafer holder.

Unless otherwise noted in a Table, each stripper solution was heated to93° C. and a wafer piece immersed. The timer was started as soon as theywere fully immersed. Immersion was maintained 75 minutes, after whichthe wafer was rinsed with DI water and dried.

Samples were evaluated as clean (C) if substantially all residues hadbeen removed from the tops and sidewalls of the solder pillar and noorganic resist pieces re-deposited on any part of the field of thewafer. Samples were evaluated as not clean (NC) if substantially allmaterials had not been removed. Not clean (NC) does not mean that nocleaning at all had occurred. Results are recorded in Table 2.

In addition to the residues described above, each patterned test waferhad a variety of materials, including copper metal, a tin/silveramalgam, and cured polyimide damaged by an oxidizing plasma. Asuccessful solution must remove the residues while maintainingcompatibility with all other materials on the wafer surface. Metalcompatibility was concluded based on SEM imaging of the samples.Polyimide compatibility was concluded based on two tests: (1) SEMimaging of samples and if (1) showed compatibility, then (2) comparisonof the polyimide FTIR spectrum on blanket PI wafers, exposed to the sameplasma treatment as the wafer, prior to immersion and after immersion.Comparison of spectra before and after indicated if any change inchemical composition or thickness, calculated based on spacing ofinterference fringes, occurred. Results are summarized in Table 2. WhereN/A is indicated, the solution is not deemed useful for cleaning becauseit is not stable, and therefore, no cleaning tests are warranted.

TABLE 2 Example 1 Solution Example 2 Example 2 Characteristics CleaningSample Compatibility Formulation Clarity Precipitate CharacteristicsMetals Polyimide [1] Clear Insignificant Clean Compatible not compatibleby SEM [2] Clear Insignificant Clean Compatible not compatible by SEM[3] Clear Insignificant Not clean under N/A N/A these test conditions[4] Clear Insignificant Clean Compatible Compatible by SEM and FTIR [5]Clear Insignificant Clean Compatible Not compatible by SEM [6] Clear YesN/A N/A N/A [7] Clear Yes N/A N/A N/A [8] Clear Yes N/A N/A N/A

Example 3

The components for the formulations tested, [9-25] in the followingExamples were combined with stirring at room temperature to give between300 g of a homogenous stripper solution. Solution homogeneity requiresthe KOH to be blended into the appropriate co-solvents prior to additionof DMSO. The surfactant is added into the blend last. The solution washeated to 93° C., with slow agitation for 2 hours. 93° C. was selectedas an extreme temperature to exacerbate any stability problems thatcould occur. The timer was started when the solution reached the desiredtemperature. The solution was then removed from the heat source and leftto cool to room temperature, 23° C. Observations about solution clarityand amount of precipitate were recorded in Table 3.

Example 4

The components for the formulations tested in the following Examples[9-25] were combined with stirring at room temperature to give between100 g of a homogenous stripper solution. Solution homogeneity requiresthe KOH to be blended into the appropriate co-solvents prior to additionof DMSO. The surfactant is added into the blend last. The solution washeated to between 93° C., with slow agitation. Patterned test waferswith solder bumps positioned as an array in a polyimide film wereobtained. The test wafers had been processed in a high energy oxidizingplasma to remove about 1-3 μm of polyimide. Residues deposited on thesides and tops of solder bumps during the plasma process were notremoved prior to these tests. The patterned test wafers were cleavedinto ˜4×3 cm pieces and mounted into a small scale wafer holder.

Unless otherwise noted in a Table, each stripper solution was heated to93° C. and a wafer piece immersed. The timer was started as soon as theywere fully immersed. Immersion was maintained 75 minutes, after whichthe wafer was rinsed with DI water and dried. Results are recorded inTable 3.

In addition to the residues described above, each patterned test waferhad a variety of materials, including copper metal, a tin/silveramalgam, and cured polyimide that had been damaged by the oxidizingplasma. A successful solution must remove the residues while maintainingcompatibility with all other materials on the wafer surface. Metalcompatibility was concluded based on SEM imaging of the samples.Polyimide compatibility was concluded based on two tests: (1) SEMimaging of samples and if (1) showed compatibility, then (2) comparisonof the polyimide FTIR spectrum on blanket PI wafers, exposed to the sameplasma treatment as the wafer, prior to immersion and after immersion.Comparison of spectra before and after indicated if any change inchemical composition or thickness, calculated based on spacing ofinterference fringes, occurred. Results are summarized in Table 3.

TABLE 3 Solution Characteristics Cleaning Sample CompatibilityFormulation Clarity Precipitate Characteristics Metals Polyimide [9]Clear Yes N/A N/A N/A DMSO, 81%; MEA, 2.8; MMB 6.7%; THFA, 3.8%; Phenolethoxylate, 4.7%, KOH, 0.9%, H₂O 0.1% [10] Clear Insignificant CleanDMSO, 80%; MEA, 2.8; MMB 6.7%; THFA, 3.8% Phenol ethoxylate, 4.7; KOH,1.8%; H₂O, 0.2% [11] Clear Yes N/A N/A N/A DMSO, 79.2%; MEA, 2.8; MMB6.7%; THFA, 3.8%; Phenol ethoxylate, 4.7; KOH, 2.5%; H₂O 0.3% [12] ClearInsignificant Clean Compatible Compatible DMSO, 78.2%; MEA, using SEM2.8; MMB 6.7%; THFA 3.8%; Phenol ethoxylate, 7; KOH, 1.2%; H₂O 0.3% [13]Slightly Insignificant Not tested but Not tested Not tested DMSO, 84.2%;MEA, hazy predicted clean, but but predicted 2.8; MMB 6.7%; THFA (withinboundaries predicted compatible 3.8% of examined compatible Phenolethoxylate, 1; formulation KOH, 1.2%; H₂O, 0.3% window) [14] Cloudy YesN/A N/A N/A DMSO, 78.3%; MEA, 5; MMB 6.7%; THFA, 3.8% Phenol ethoxylate,4.7; KOH, 1.2%; H₂O, 0.3% [15] Cloudy Yes N/A N/A N/A DMSO, 73.3%; MEA,10; MMB 6.7%; THFA, 3.8% Phenol ethoxylate, 4.7; KOH, 1.2%; H₂O, 0.3%[16] Clear Insignificant Clean Compatible Compatible DMSO, 78.3%; MEA,using SEM 2.8; MMB 6.7%; THFA, 6% Phenol ethoxylate, 4.7; KOH, 1.2%;H₂O, 0.3% [17] Clear Insignificant Clean Compatible Compatible DMSO,76.3%; MEA, using SEM 2.8; MMB 6.7%; THFA, 8% Phenol ethoxylate, 4.7;KOH, 1.2%; H₂O, 0.3% [18] Clear Insignificant Clean CompatibleCompatible DMSO, 84.2%; MEA, using SEM 2.8; MMB 3%; THFA, 3.8% Phenolethoxylate, 4.7; KOH, 1.2%; H₂O, 0.3% [19] Clear Insignificant CleanCompatible Compatible DMSO, 79.2%; MEA, using SEM 2.8; MMB 8%; THFA,3.8% Phenol ethoxylate, 4.7; KOH, 1.2%; H₂O, 0.3% [20] Clear Yes N/A N/AN/A DMSO, 77.2%; MEA, 2.8; MMB 10%; THFA, 3.8% Phenol ethoxylate, 4.7;KOH, 1.2%; H₂O, 0.3% [21] Clear Yes N/A N/A N/A DMSO, 72.2%; MEA, 2.8;MMB 15%; THFA, 3.8% Phenol ethoxylate, 4.7; KOH, 1.2%; H₂O, 0.3% [22]Clear Yes N/A N/A N/A DMSO, 79.5%; MEA, 2.8; MMB 6.7%; THFA, 3.8%;Phenol ethoxylate, 4.7; KOH, 1.2%; H₂O 1.3% [23] Clear Yes N/A N/A N/ADMSO, 77.5%; MEA, 2.8; MMB 6.7%; THFA, 3.8%; Phenol ethoxylate, 4.7;KOH, 1.2%; H₂O, 3.3% [24] Clear Yes N/A N/A N/A DMSO, 75.5%; MEA, 2.8;MMB 6.7%; THFA, 3.8% Phenol ethoxylate, 4.7; KOH, 1.2%; H₂O, 5.3% [25]Hazy Gelled N/A N/A N/A NMP, 80.5%; MEA, 2.8; MMB 6.7%; THFA, 3.8%Phenol ethoxylate, 4.7; KOH, 1.2%; H₂O, 0.3%

Example 5

Formulation [4], Table 1 was tested in the following Examples ofcleaning with different immersion processes. The solution was combinedwith stirring at room temperature to give about 100 g of a homogenousstripper solution. Solution homogeneity requires the KOH to be blendedinto the appropriate co-solvents prior to addition of DMSO. Thesurfactant is added into the blend last. The solution was heated to thetarget temperature, with slow agitation. Patterned test wafers withsolder bumps positioned as an array in a polyimide film were obtained.The test wafers had been processed in a high energy oxidizing plasma toremove about 1-3 μm of polyimide. Residues deposited on the sides andtops of solder bumps during the plasma process were not removed prior tothese tests. The patterned test wafers were cleaved into ˜4×3 cm piecesand mounted into a small scale wafer holder.

The stripper solution was heated between 70° C. and 93° C. and a waferpiece immersed. The timer was started as soon as they were fullyimmersed. Immersion was maintained 60 or 75 minutes, after which thewafer was rinsed with DI water and dried. Results are recorded in Table4.

In addition to the residues described above, each patterned test waferhad a variety of materials, including copper metal, a tin/silveramalgam, and cured polyimide that had been damaged by the oxidizingplasma. A successful solution must remove the residues while maintainingcompatibility with all other materials on the wafer surface. Metalcompatibility was concluded based on SEM imaging of the samples.Polyimide compatibility was concluded based on two tests: (1) SEMimaging of samples and if (1) showed compatibility, then (2) comparisonof the polyimide FTIR spectrum on blanket PI wafers, exposed to the sameplasma treatment as the wafer, prior to immersion and after immersion.Comparison of spectra before and after indicated if any change inchemical composition or thickness, calculated based on spacing ofinterference fringes, occurred. Results are summarized in Table 4.

TABLE 4 Process Information Temperature Time Cleaning SampleCompatibility Formulation (° C.) (min) Characteristics Metals Polyimide[4] 93 75 Clean Compatible Compatible by SEM and FTIR [4] 80 75 CleanCompatible Compatible by SEM and FTIR [4] 70 75 Not clean under N/A N/Athese test conditions [4] 80 60 Clean Compatible Compatible by SEM andFTIR

What we claim is:
 1. A solution to clean a wafer comprising: a polaraprotic solvent, an inorganic base; a co-solvent for said inorganicbase; a unsaturated cycloaliphatic compound having a ring ether groupand at least one substituent bearing a primary hydroxyl group; anorganic base comprising an amine compound; and a nonionic surfactantbearing at least one ether group, wherein the solution has a flash pointabove an operational temperature used to clean the wafer.
 2. The processof claim 1, wherein the flash point is at least 80° C.
 3. The process ofclaim 1, wherein the solution has a viscosity of less than 20 centipoiseat 25° C.
 4. A process for cleaning a semi-conductor wafer comprisingproviding etched wafer containing metal pillars, contacting the etchedwafer with a cleaning solution, removing the wafer from the cleaningsolution, wherein the resulting wafer is substantially free of post etchresidues and photoresist residues without etching the metal pillars bythe cleaning solution.
 5. The process of claim 4, wherein contact isobtained by immersing the wafer into a cleaning solution.
 6. The processof claim 4, wherein the solution comprises: A. a polar aprotic solvent,B. an inorganic base; C. a co-solvent for said inorganic base; D. aunsaturated cycloaliphatic compound having a ring ether group and atleast one substituent bearing a primary hydroxyl group; and E. anorganic base comprising an amine compound.
 7. The process of claim 4,wherein the polar aprotic solvent comprises a C₁-C₄ dialkyl sulfoxide.8. The process of claim 4, wherein the solution contains less than 3weight percent pyrrolidone compounds.
 9. The process of claim 4, whereindimethyl sulfoxide is present in an amount within a range of 60 wt. % to90 wt. %.
 10. The process of claim 4, wherein the polar aprotic solventis a type present in an amount effective to remove: (i) uncuredpolyimide photoresist from a semiconductor wafer and (ii) polyimidepolymer residues that have been subjected to a plasma etching process,at one or more temperatures within a range of 78° C. to 90° C. andwithin 30 seconds when immersed in the solution.
 11. The process ofclaim 4, wherein the inorganic base comprises a hydroxide of a Group Ior Group II metal.
 12. The process of claim 11, wherein the inorganicbase comprises a hydroxide of a Group I metal.
 13. The process of claim11, wherein the inorganic base comprises potassium hydroxide.
 14. Theprocess of claim 4, wherein the solution does not precipitate solidscontaining the metal of the inorganic base upon heating to 93° C. andwithin a 4 hour cool down period in ambient conditions.
 15. The processof claim 4, wherein the inorganic base comprises potassium hydroxidepresent in an amount of at least 1.0 wt. % and up to 2.5 wt. %.
 16. Theprocess of claim 4, wherein the solution does not contain added lithiumhydroxide.
 17. The process of claim 4, wherein the co-solvent comprisesa glycol ether compound having at least one ether group and at least onehydroxyl group.
 18. The process of claim 17, wherein the glycol etherhas a molecular weight of less than
 150. 19. The process of claim 4,wherein the co-solvent comprises a glycol ether having one ether groupand one hydroxyl group.
 20. The process of claim 4, wherein theco-solvent comprises ethyleneglycol monomethyl ether, ethyleneglycolmonoethyl ether, propylene glycol monomethyl ether, diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, diethylene glycolmonopropyl ether, diethylene glycol monobutyl ether, dipropylene glycolmonobutyl ether, dipropylene glycol monopropyl ether, tripropyleneglycol monomethyl ether, tripropylene glycol monobutyl ether,propyleneglycol butyl ether, ethylene glycol monohexyl ether,ethyleneglycol mono-2-ethylbuyl ether, triethyleneglycol monobutylether, tetraethyleneglycol monobutyl ether, or tetrapropyleneglycolmonobutyl ether.
 21. The process of claim 4, wherein the co-solventcomprises 3-methoxybutanol; 3-methyl-3-methoxybutanol; or3-methyl-1,3-butanediol.
 22. The process of claim 4, wherein theco-solvent is present in the solution in an amount of at least 4 wt. %and up to 8 wt. %.
 23. The process of claim 4, wherein said unsaturatedcycloaliphatic compound comprises a compound represented by thefollowing general formula (X):

wherein R14 and R15 are independently hydrogen, a hydroxyl group, or aC1-C8 alkyl group having one or more primary or secondary hydroxylgroups, provided that R14 and R15 are not both hydrogen and are not bothhydroxyl groups.
 24. The process of claim 4, wherein said unsaturatedcycloaliphatic compound comprises tetrahydrofurfuryl alcohol, furfurylalcohol, or a combination thereof.
 25. The process of claim 4, whereinsaid unsaturated cycloaliphatic compound is effective to remove residueson the tops of solder bumps on a semiconductor wafer subjected to plasmaetching.
 26. The process of claim 4, wherein the unsaturatedcycloaliphatic compound is present in the solution in an amount rangingfrom 1 wt. % to 8 wt. %.
 27. The process of claim 4, wherein thesolution comprises: A. dimethyl sulfoxide, B. potassium hydroxide, C. aco-solvent represented by the following formula (IX):

wherein R1 and R3 are each independently be a hydrogen atom or a C1-C4alkyl group, and R2 is a C1-C4 alkyl group, D. a cycloaliphatic compoundhaving a furfuryl moiety, E. an alkanolamine, and F. a polyoxyethyleneof phenol or an alkylphenol.
 28. The process of claim 4, wherein theorganic base comprises an alkanolamine having at least two carbon atoms,at least one nitrogen atom, and at least one hydroxyl group, thenitrogen atom and hydroxyl group being attached to different carbonatoms.
 29. The process of claim 4, wherein the organic base comprisesethanolamine, N-methylethanolamine, N-ethylethanolamine,N-propylethanolamine, diethanolamine, triethanolamine,N-methyldiethanolamine, N-ethyldiethanolamine, isopropanolamine, ordiisopropanolamine.
 30. The process of claim 4, wherein the organic baseis present in an amount ranging from 1 wt. % to 5 wt. %.
 31. The processof claim 4, further comprising a nonionic surfactant.
 32. The process ofclaim 4, wherein the surfactant has a molecular weight of greater than200 and less than
 1000. 33. The process of claim 32, wherein the amountof surfactant is at least 1 wt. % and up to 10 wt. %.
 34. The process ofclaim 32, wherein the surfactant comprises an aromatic ring having atleast one substituent, said-substituent containing —(C2H4O)— moieties.35. The process of claim 32 wherein the surfactant comprises a compoundhaving a phenolic ethoxylate moiety.
 36. The process of claim 32,wherein the surfactant comprises an aromatic ring having at least onesubstituent, said substituent containing —(C2H4O)_(p)— moieties, whereinp is an integer within a range of 2 to
 8. 37. The process of claim 32,wherein the surfactant comprises an aromatic ring having a firstsubstituent containing —(C2H4O)— moieties and a second substituentcomprising a branched or unbranched, saturated or unsaturated, C₁-C₂₂alkyl group.
 38. The process of claim 4, wherein the solution containsnot more than 2 wt. % water based on the weight of the solution.